Vaporizing device and method

ABSTRACT

A vaporizing nozzle comprises a wall of porous material, for example sintered bronze, through which the liquid to be evaporated percolates. The liquid may be, for example, petrol. At the other side of the wall the liquid atomizes or vaporizes into a gas stream, for example an air stream. The nozzle therefore provides a simple and convenient way of vaporizing or atomizing a liquid within a gas stream in, for example, the vaporization of petrol into an air stream for use with internal combustion engines. The nozzle includes selectively closed machined portions for altering the flow characteristics of the material.

FIELD OF INVENTION

This invention relates to a vaporising device and in particular relatesto a device useful in evaporating liquid into gaseous streams forexample liquid fuels into an air stream.

BACKGROUND OF INVENTION

In internal combustion engines, turbines, liquid fuel fired furnaces,and the like, liquid fuel is mixed with an oxidising gas stream, forexample an air stream. In a conventional fuel/air mixing device such asa carburettor the fuel discharges from a jet or metering bar in a streamwhich is torn apart into ligaments which progressively break up andcontract into droplets of various sizes. During this processvaporisation takes place and the droplets progressively reduce in sizethe finest vaporising completely. Ideally, all of the liquid dropletswould be vaporised and uniformly distributed in the air stream by thetime they reach the combustion zone or combustion chamber.

In practice, especially under the varying conditions which internalcombustion engines in particular are subjected to, some of the dropletsare incompletely vaporised and this has adverse effects on both fueleconomy and the cleanliness of the exhaust gases. In most conventionaldevices such as carburettors complete vaporisation only occurs at somepart throttle conditions. Furthermore vaporisation occurs at asubstantial distance away from the point of fuel discharge whichdistance varies with variable fuel demands of the engine. Fuelvaporasation is improved with forced fuel injection systems where thefuel injection nozzle functions to mechanically atomise the fuel at thetip exposed to the air stream. Fuel injection has several advantagesover conventional carburettors but suffers from the disadvantages ofhigh manufacturing costs and additional complexity requiring moresophisticated servicing.

The invention seeks to provide a form of vaporising device improved inthe above respects.

SUMMARY OF INVENTION

According to the present invention there is provided a vaporising devicewhich comprises a nozzle located in a gaseous stream such that a smallportion of the stream passes through the nozzle, the nozzle comprising awall of porous material being a sintered metal through which the liquidto be vapourised percolates from one side thereof into the gas streamthrough the nozzle and wherein the surface of the sintered metal isselectively closed by machined portions of the surface thereof.

The porous material is a sintered metal, in particular brass, bronze,cupro-nickel or the like. Conveniently, the wall will be cylindrical inconfiguration and the gas stream may flow over the cylinder, in whichcase the liquid will be supplied internally of the cylinder, or may flowthrough the cylinder, in which case the liquid will be suppliedexternally of the cylinder.

The primary use of the device of the invention is envisaged to be inmixing hydrocarbon fuels with an air stream, for use in for example aninternal combustion engine, and the terms `fuel` and `air stream` willbe used hereafter but it will be appreciated that the device of theinvention is useful wherever a liquid is to be evaporated in to a gasstream.

In a preferred form of manufacturing a device in accordance with theinvention the applicants have utilised a property of sinterednon-ferrous metals hitherto regarded as a disadvantage. A sintered metaltube or cylinder, for example of a type available for use in filtrationsystems, cannot normally be machined since machining of the sinteredmetal surface causes the porous porosity of the surface to be lost sincethe physical cutting action of the machine tool causes the sphericalgrains of the sintered material to flatten and close the interstices.Thus, by selectively machining portions of a cylinder of sinteredmaterial the surface area can be varied at will. Thus, as will bedescribed more fully heriafter, the flow characteristics of a cylinderof sintered material can be altered to provide a nozzle having thenecessary fuel delivery characteristics for a particular end use.

FIGURES IN THE DRAWINGS

The invention will be described further, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic sectional and plan view of the nozzle of adevice in accordance with the invention;

FIG. 2 is a diagrammatic representation of the properties of the nozzleof FIG. 1;

FIG. 3 is a sectional view of an embodiment of the device of theinvention for supplying fuel to an internal combustion engine;

FIG. 4 is a diagrammatic view of a further embodiment;

FIG. 5 is a diagrammatic representation of an application of the deviceof the invention in a ramjet combustor; and

FIG. 6 is a diagrammatic representation of a device of the invention ina booster venturi.

PREFERRED EMBODIMENT

Referring to the drawings, FIG. 1 illustrates the basic principle of thedevice of the invention. In this, a nozzle generally designated 10comprises a cylinder of sintered material such as bronze 12. Thecylinder 12 is machined on its external surface at 14, 16 and 18employing a small depth of cut. A cutting depth of 1/100th of an inch orless has been found to be adequate for sintered bronze of grain sizefrom 2.1/2 to 5 microns. The machining effectively closes the poroussurface at 14, 16 and 18. The two unmachined portions 20 remain porous.Similarly, internally of the cylinder, portions 22 are machined leavingporous the portion 24.

The axial width of the portion 24 is calculated in relation to theinternal diameter of the cylinder, the porosity of the porous material,and the fuel requirements so as to allow sufficient fuel to percolatethrough towards the outer wall surface. Fuel is fed internally of thenozzle 10 from either end, the other end being blocked off, and passesthrough the strip portion 24 into the porous wall 12 as indicated by thearrow. Since the porous external surfaces 20 are offset with respect tothe internal surface 24 there is some axial movement of the fuel beforeit reaches the porous surface portions 20 where it escapes to the airstream indicated at 26. It will be observed that the total surface areaof the exit portions 20 is considerably greater than that of the fuelinlet portion 24 and this is illustrated diagrammatically in FIG. 2where the pressure drop in the nozzle body is illustrated graphically.Thus the fuel is presented to a large porous surface area in the airstream 26 and therefore enters the air stream 26 in the form of amultiplicity of extremely fine droplets which rapidly vaporise.

In order to obtain the correct fuel/air ratio it is not necessary topass the total air stream over the nozzle and indeed only a smallportion of the air stream will be passed over the nozzle and theresultant rich air/fuel mixture will then be mixed with further airbefore moving into the combustion zone. One advantage of thisarrangement is that if it is necessary, for example in the case ofheavier fuels such as paraffins and diesel fuels, to aid evaporation byheating either the air stream, passing through the nozzle 26, or thenozzle casing 40. Then the whole of the air stream need not be heatedbut only the small proportion passing over the nozzle. Thus the heatingrequirements are far less than would otherwise be the case andvolumetric efficiency of the engine is thereby improved.

Fuel is drawn from the nozzle in a similar manner to the way in which itis drawn from the jet of a conventional carburettor. However, in thelatter case, fuel leaves the jet in the form of a stream which must bebroken up and atomised in the air stream, fuel leaves the nozzle 26already in the form of fine droplets and vapour since it is leaving asurface much larger than the entry surface.

Referring now to FIG. 3 an embodiment of the invention suitable for usewith an internal combustion engine is shown in more detail.

In this case the nozzle generally designated 100 comprises a body 30within which is included a cylindrical portion 32 of porous sinteredmaterial. Within the body 30 is a fuel supply line 34 connected by meansof one or more passageways 36 to an annular space 38 immediatelyadjacent the inner surface of the porous cylinder 32. The cylinder 32will have been machined in a like manner to that described with respectto FIG. 1 in accordance with the operating requirements of the enginewith which the nozzle is to be used. The nozzle 100 is mounted within ahousing 40 which defines an air space 42 between the inner surface ofthe housing and the outer surface of the cylinder 32. The forward end ofthe nozzle 100 is provided with an inclined surface 44 adapted to matewith a complementary surface 46 within the housing 40. Movement of thenozzle body backwards and forwards as represented by arrow A moves thenozzle 100 into and out of engagement with the surface 46 therebyaccurately metering the flow of fuel/air mixture from the space 42. Airis fed to the space 42, for example via variable excess air passages 48and an air inlet diffuser 49, and fuel/air mixture leaves the housing 40at exit 50. The diffuser 49 comprises a porous disc fitted to the inletend of the housing 40. The purpose of the diffuser 49 is to provide auniform envelope of air around the cylindrical portion 32. The passage48 are variable and may be used to adjust the excess air supply.

The device of FIG. 3 is mounted in the inlet manifold of an internalcombustion engine. Air is fed via the inlets 48 to the annular space 42where it passes over the external surface of the porous cylinder 32entraining droplets of fuel. The fuel/air mixture passes through the gapbetween the surfaces 44 and 46 and leaves via the exit 50 on route tothe combustion zone. Fuel is passed through the fuel inlet 34 andpassage or passages 36 into the annular space 38 where it percolates, asdescribed more fully in relation to FIG. 1 above, through to the exitsurfaces in the air stream. The speed of the air stream, and thereforethe pressure drop caused by it, will vary the amount of fuel drawn in asimilar manner to a conventional carburettor. The amount of fuel and airflow is regulated by moving the nozzle 100 backwards and forwards andtherefore varying the gap between the mating surfaces 44 and 46. Asshown in FIG. 3 the mating surfaces are in contact with each othershutting off the fuel/air flow completely. The mechanism for moving thenozzle body is not illustrated but this may be accomplished in anysuitable manner, for example in a similar manner to a poppet valve.

FIG. 4 illustrates a form of nozzle where a machined cylinder ofsintered material is inserted within a venturi. In this case the airflow is internally of the cylinder and the fuel is supplied to theexternal surface.

In FIG. 5 a ring of devices 10 in accordance with the invention isillustrated in a ramjet combuster. After burner jets are provided whichmay also be in accordance with the invention.

Yet another application is illustrated in FIG. 6 where a jet inaccordance with the invention is incorporated into a booster venturi.The jet 100 is similar to that illustrated in FIG. 3 but is locatedwithin a booster venturi in turn within a main venturi. Once again theoperation is a before.

It has been found that sintered materials of various pore sizes areuseful in the facts of the invention. Pore sizes of 2.5 and 5 micrometerhave been found suitable for applications in which petrol is the fuelconcerned whereas materials having a pore size of 12.5 micrometers aremore suitable for the heavier fuels such as diesel. Particularly forsintered materials with larger pore sizes, machining may not completelyclose off the porosity of the surface. In these circumstances it may benecessary to use additional sealing such as solder or chemical sealingcompounds such as adhesives.

The devices of the invention can be used as a replacement for the jetsin conventional carburettors but with their faster vaporisationcharacteristics they may advantageously be located closer to thecombustion zones or engine cylinders. Thus one or more devices of theinvention may advantageously be located adjacent the cylinder of amulticylinder internal combustion engine. In this configuration thedevices of the invention give a similar performance to fuel injectionsystems but at a considerably lower cost. The fast vaporisation of thenozzle ensures easy starting of any internal combustion engine withwhich they are fitted and also more complete combustion lesseningpollution products in the engine exhaust. The devices of the inventionmay also be used with advantage in other burning situations such asliquid fuel fired furnaces, turbines and the like including cryogenicapplications for example in rockets.

I claim:
 1. A vaporising device which comprises a nozzle located in agaseous stream such that a small portion of the stream passes throughthe nozzle, the nozzle comprising a wall of porous material being asintered metal through which the liquid to be vapourised percolates fromone side thereof into the gas stream through the nozzle, said materialhaving a surface, and wherein the surface of the sintered metal includesselectively closed machined portions for altering the flowcharacteristics of said material.
 2. A device as claimed in claim 1 inwhich the wall is cylindrical in configuration and the portion of thegas stream flows over the cylinder, with the liquid being suppliedinternally of the cylinder.
 3. A device as claimed in claim 1 in whichthe area selected for machining is chosen to suit the characteristicdesired for evaporating a particular liquid into the gas stream.
 4. Adevice as claimed in claim 1 wherein the porous material is a sinteredmetal having spherical grains.
 5. A device as claimed in claim 4 inwhich the sintered metal is bronze of a grain from two-and-a-half tofive microns.
 6. A device as claimed in claim 1 in which the metal isnon-ferrous.
 7. A device as claimed in claim 6 in which the metal isbrass, bronze or cupro-nickel.
 8. A method of forming a vaporizingdevice, said method including the steps of: forming a wall having asurface of porous material of sintered metal having predetermined flowcharacteristics, and altering the flow characteristics by machiningselective portions of the surface closed.